Using binocular rivalry for expanding color perception

ABSTRACT

An article includes a first ophthalmic lens including a first spectral filter (e.g., a reflective or absorptive spectral filter), and a second ophthalmic lens including a second spectral filter (e.g., a reflective or absorptive spectral filter). The first spectral filter substantially blocks visible light having wavelengths corresponding to a first portion of a spectral sensitivity range of a first type of cone (e.g., S, M, or L cone) and substantially passes visible light having wavelengths in a second, non-overlapping portion of the spectral sensitivity range. The second spectral filter substantially blocks visible light having wavelengths in the second portion of the spectral sensitivity range and substantially passes visible light having wavelengths in the first spectral sensitivity range.

BACKGROUND

A human eye detects light through rods and cones located in the retina.Rods are photoreceptors that are sensitive to low level of light, but donot discriminate between colors. Cones are photoreceptors with colorpigments that selectively transmits a certain spectrum of the incominglight. Cones are one of the three types: S-cones, M-cones, and L-cones.S-cones, where S stands for short, have peak responsivity around 420 nm.M-cones, where M stands for medium, have peak responsivity around 530nm. L-cones, where L stands for long, have peak responsivity around 570nm.

The human visual system perceives color by processing the differences inthe stimulation of the three types of cones. For example, yellow isperceived when an image formed on the retina stimulates L-cones morethan the M-cones, as L-cones have a peak responsivity around 570 nm thatfalls within the interval of wavelength (560 nm-590 nm) that a persontypically associates with color yellow. In another example, green isperceived when the image formed on the retina stimulates M-cones morethan S- or L-cones, as M-cone has peak responsivity around 530 nm thatfalls in between 520 nm-560 nm corresponding to green.

Color blindness is a decreased ability to see color or distinguishcolors in a human vision. It ranges in its severity, ranging from ageneral lack of color vision (‘monochromatism’), to a malfunction of oneof the three types of cones (‘dichromacy’), to an anomalous spectralsensitivity in one or more pigments of a cone that results in decreasedability to differentiate between pairs of colors. Protanomaly, forexample, occurs in a person who is missing or has malfunctioningL-cones. Deuteranomaly occurs where the person has missing ormalfunctioning M-cones. Tritanomaly is caused by missing ormalfunctioning S-cone.

SUMMARY

In general, in a first aspect, the invention features an article thatincludes a first ophthalmic lens including a first spectral filter(e.g., a reflective or absorptive spectral filter), and a secondophthalmic lens including a second spectral filter (e.g., a reflectiveor absorptive spectral filter). The first spectral filter substantiallyblocks visible light having wavelengths corresponding to a first portionof a spectral sensitivity range of a first type of cone (e.g., S, M, orL cone) and substantially passes visible light having wavelengths in asecond, non-overlapping portion of the spectral sensitivity range. Thesecond spectral filter substantially blocks visible light havingwavelengths in the second portion of the spectral sensitivity range andsubstantially passes visible light having wavelengths in the firstspectral sensitivity range.

Embodiments of the article can include one or more of the followingfeatures. For example, the article can be eyeglasses, a pair of contactlenses, goggles, or a pair of intraocular lenses.

In some embodiments, the first and second spectral filters are alow-pass filter and a high-pass filter, respectively. In certain cases,at least one of the first and second spectral filters is a notch filter.

At least one of (e.g., both of) the first and second spectral filterscan substantially transmit visible light having wavelengths below 520nm. In certain cases, both of the first and second spectral filterssubstantially transmits visible light having wavelengths below 520 nm.

First and second spectral filters can be implemented in various ways.For example, the first and second spectral filters can be reflectivespectral filters. As another example, the first and second spectralfilters are absorptive spectral filters.

In some embodiments, the first and second spectral filters are passivespectral filters.

In some embodiments, the first and second spectral filters dynamicspectral filters. In certain cases, the dynamic spectral filters eachinclude an electro-optic element.

In some embodiments, at least the first ophthalmic lens further includesa filter array that includes the first spectral filter. In certaincases, the second ophthalmic lens further includes a filter array thatincludes the second spectral filter.

In some embodiments, a first transmission spectrum of the first spectralfilter and a second transmission spectrum of the second spectral filterare configured to enhance the color perception of a dichromat.

In general, in a further aspect, the invention features a method ofenhancing the color perception of a dichromat that includes providingthe dichromat with the article of claim 1.

In some implementations, the dichromat is a protanope and the first typeof cone corresponds to the M-cone. In certain cases, the dichromat is adeuteranope and the first type of cone is the L-cone. In certain cases,the dichromat is a tritanope and the first type of cone is the S-cone.The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

As used herein, “substantially blocks” and “substantially transmits” or“substantially passes” generally refers to a level of blocking andtransmitting/passing of light that is perceptible to the human eye.Substantially blocking, for example, can include blocking of 90% or more(e.g., 95% or more, 98% or more, 99% or more) of the designated lightfrom a receptor. Substantial transmission, for example, can includetransmission of 50% or more (e.g., 75% or more, 90% or more, 95% ormore) of the designated light to a receptor.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a pair of eyeglasses that include spectral filters forenhancing color perception.

FIG. 2 shows peak-normalized spectral responsivity curves of S-, M-, andL-cones.

FIG. 3 shows an example of effective spectral responsivity curves of S-and M-cones as modified by color-perception enhancing lens designed fora protanope.

FIG. 4 shows an example of effective spectral responsivity curves of S-and L-cones as modified by color-perception enhancing lens designed fora deuteranope.

FIG. 5 A-B show examples of effective spectral responsivity curves of S-and M-cones as modified by color-perception enhancing lens designed fora protanope using a notch filter.

FIG. 6 A-B show examples of effective spectral responsivity curves of S-and L-cones as modified by color-perception enhancing lens designed fora deuteranope using a notch filter.

FIG. 7 A-B show examples of effective spectral responsivity curves of M-and L-cones as modified by color-perception enhancing lens designed fora tritanope.

FIG. 8 A-B show examples of effective spectral responsivity curves ofS-, M-, and L-cones as modified by color-perception enhancing lensdesigned for a trichromat.

FIG. 9 shows an embodiment of eyeglasses featuring side-shielding forreducing backside reflection.

FIG. 10 shows a schematic cross-section of a lens of color-perceptionenhancing eyeglasses implementing a backside reflection reduction layer.

FIG. 11 shows a pair of eyeglasses that include spectral filter arraysfor enhancing color perception.

FIG. 12 shows a pair of eyeglasses that include dynamic spectral filtersfor enhancing color perception.

FIGS. 13A-B show examples of effective spectral responsivity curves ofS- and M-cones as modified by color-perception enhancing lensimplemented for a protanope.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1, a pair of color-perception enhancing eyeglasses 100are disclosed which can enable a dichromatic person (a ‘dichromat’) todifferentiate a third color. Eyeglasses 100 includes frames 101 andophthalmic lenses 110 and 120. Each ophthalmic lens includes a differentspectral filter. Eyeglasses 100 enhance the wearers color perception byusing the concept of binocular rivalry. This works byspectrally-filtering light differently for each eye so that the sametype of cone is responsive to different wavelengths in one eye versusthe other. Specific examples of spectral filters are discussed below.

Binocular rivalry is a perceptual ‘rivalry’, or competition, that occurswhen two different images are presented simultaneously to the two eyes.In such scenario, our visual perception initially suppresses one of thetwo images and makes the other image dominant. The perceptual dominance,however, switches after a few seconds and only the other image is ‘seen’during this time. This rivalry continues on as long as the conflictingvisual stimulus remains, switching between the images present at the twoeyes every few seconds.

A binocular rivalry-like effect is believed to exist for colors. Forexample, when a green square is shown to the left eye while a bluesquare is shown to the right eye, the human visual system processes thisinformation and perceives it as cyan resulting from mixing of green andblue, although the individual images are not in cyan. This type ofeffect can be used in enhancing human color perception.

Normal human color perception is provided by presence of the three typesof cones in each retina. FIG. 2 shows a plot of the peak-normalizedspectral responsivity curves 210, 220 and 230 of the S-, M-, andL-cones, respectively. The S-cones have peak sensitivity atapproximately 440 nm. The M-cones have peak sensitivity at approximately550 nm, and the L-cones have peak sensitivity at approximately 570 nm.These three cones correspond approximately to the three principle colorcomponents of human color perception. A malfunction or omission of anyone of these three cones results in decreased ability to perceivecolors, as is the case for dichromats. It is believed, however, that thedimensionality of a dichromat's color vision can be improved byproviding different spectral filtering to each eye.

A protanope has difficulty perceiving the difference between green andred due to lack of L-cone functionality, which is responsible forperception of red in a trichromat. An appropriate set of filters can beapplied to protanope's eyes to create a difference in effective spectralresponsivity curve of the M-cone between the left and the right eye,potentially enhancing his or her color perception. For a protanope, onefiltering strategy is to effectively make the M-cone in one eyesensitive only to the shorter wavelengths of the M-cone, such aswavelengths below 550 nm (call this ‘new’ cone an M′-cone), and M-conein the other eye sensitive only to the longer wavelengths of the M-cone,such as wavelengths above 550 nm (call this ‘new’ cone a L′-cone). Inthis scenario, one eye now has S- and M′-cones, and the other eye hasL′-cone. When the two images from the eyes are processed by the humanvisual system, it is believed that one is able to distinguish colorsthat he or she otherwise cannot with just the S- and M-cones. Whileselecting a filter for modifying M-cone responsivity, it is important tomaintain the integrity of S-cone's responsivity in at least one eye topreserve blue color perception. The integrity of the S-cone'sresponsivity can be maintained by ensuring that the filter configurationhas a passband over spectral responsivity curve 210.

An example of filter transmission characteristics desirable for aprotanope can be achieved by the following. Referring to FIG. 3, plot300 shows portions of normalized responsivity curves 210 and 220 of theS- and M-cone from FIG. 2, but omits normalized responsivity of L-cone230, as a protanope does not have functioning L-cones. The objective isto create a third responsivity curve from that of the two cones, whereinthe resulting peaks of the three curves are separated from each other.Such filtering can be achieved by using a short-pass filter 330 for oneeye with its transmission window marked by the labeled dotted box, whichpasses wavelength shorter than a cutoff wavelength. The eyeglassesinclude a long-pass filter 340 for the other eye, with its transmissionwindow marked by the labeled dotted box, which passes wavelength longerthan a cutoff wavelength. By selecting a short-pass filter with a cutoffwavelength around the peak responsivity of an M-cone and placing it infront of one eye, the filter modifies the effective spectralresponsivity of the M-cone, turning it into a M′-cone with modifiedresponsivity curve 310. By selecting a long-pass filter with a cutoffwavelength slightly longer than the cutoff wavelength of the short-passfilter 330 and placing it in front of the other eye, the filter modifiesthe effective spectral responsivity of the M-cone, turning it into aL′-cone with modified responsivity curve 320. Therefore, eyeglassesfeaturing the filters effectively create M′- and L′-cones in therespective eyes by performing a differential spectral filtering betweenthe two eyes. A consideration in filter selection is in peak separationof the resulting M′ and L′ cone responsivities. The human visual systemis typically only able to discern a difference in color when aseparation of wavelength between two colors is greater than 2-3 nm.Therefore, the short-pass and the long-pass filters should be selectedsuch that the resulting peaks of the responsivities is separated by morethan 2-3 nm (e.g., by 3 nm or more, 5 nm or more, 8 nm or more, 10 nmmore, 12 nm or more, 15 nm or more, such as about 20 nm). Generally,“peak separation” refers to the wavelength separation between themaximum sensitivity of the M′ and L′ cones. The filter transmissionwindows can be non-overlapping, touching, or overlapping to achieve thisseparation depending on the characteristics of the filters' transmissionwindows.

Another consideration is the loss in the passband of the filters. Filterpassband loss should be minimized for improved absolute spectralresponsivity of the wearer. Yet another consideration is the relativeintensity of light entering the two eyes. Pupillary response, thedilation or constriction of pupil in response to changes in brightness,does not independently control each eye. Therefore, the condition of oneeye receiving significantly less light than the other eye can causeexcessive constriction of the former and excessive dilation of thelatter, causing visual discomfort. Accordingly, filter design shouldattempt to minimize the difference in intensity of the filtered lightentering the two eyes.

While the foregoing filter combination is describing for enhancing colorperception of a protanope, other implementations are also possible. Forexample, a deuteranope also has difficulty perceiving the differencebetween green and red caused by lack of M-cone functionality, which isresponsible for perception of green in a trichromat. Similar to aprotanope, an appropriate set of filters can be applied to deuteranope'seyes to create a difference in effective spectral responsivity of theL-cone between the left and the right eye. In this case, the strategy isto effectively make the L-cone in one eye sensitive only to the shorterwavelengths of the L-cone, and L-cone in the other eye sensitive only tothe longer wavelengths of the L-cone.

An example of filter transmission characteristics desirable for adeuteranope can be achieved by the following. Referring to FIG. 4, plot400 shows portions of normalized responsivity 210 and 230 of S- andL-cone from FIG. 2, but omits normalized responsivity of M-cone 220, asa deuteranope does not have functioning M-cones. The objective is againto create a third responsivity curve from that of the two cones, whereinthe resulting peaks of the three curves are separated from each other.Such filtering can be achieved by using short-pass filter 430 with itstransmission window marked by the labeled dotted box, which passeswavelength shorter than a cutoff wavelength, and long-pass filter 440with its transmission window marked by the labeled dotted box, whichpasses wavelength longer than a cutoff wavelength. By selecting ashort-pass filter with a cutoff wavelength around the peak responsivityof an L-cone and placing it in front of one eye, the filter modifies theeffective spectral responsivity of the L-cone, turning it into a M′-conewith modified responsivity curve 410. By selecting a long-pass filterwith a cutoff wavelength slightly longer than that of the short-passfilter 430 and placing it in front of the other eye, the filter modifiesthe effective spectral responsivity of its L-cone, turning it into aL′-cone with modified responsivity curve 420. Therefore, we haveeffectively created M′- and L′-cones in the respective eyes byperforming a differential spectral filtering between the two eyes.

In some embodiments, the S-cone response is modified instead of the M-or L-cone response using a combination of filters. For example, thefilter cutoff wavelength of approximately 440 nm can be selected.

In some other embodiments, notch filters are used instead of short- orlong-pass filters. A notch filter attenuates light only within aspecified wavelength range while passing through all other visiblewavelengths within its operating window with little loss in intensity.Use of a notch filter offers an advantage over the short- and long-passfilter implementations above, which significantly reduces theresponsivity of the S-cone in one of the eyes because the long-passfilter blocks the corresponding wavelengths. In contrast, eyeglasses 100implemented using a notch filter allows the S-cone sensitivity to beretained in both eyes while creating new sets of cone responsivity fromthe L- or M-cones. In some embodiments for a protanope, referring toFIG. 5A, one filter is a notch filter with a rejection band of around500-550 nm, resulting in creation of L′-cone with responsivity curve 510by cutting off shorter wavelengths of the M-cone while retainingresponsivity of the S-cone.

Referring to FIG. 5B, the other filter is a short-pass filter with acutoff wavelength of around 550 nm, which leaves S-cone responsivityintact and creates M′-cone with responsivity curve 520 by cutting offthe longer wavelengths of M-cone.

In some embodiments, the notch filter of FIG. 5A has a rejection bandfrom 487 nm to 548 nm, and the short-pass filter of FIG. 5B has a cutoffwavelength of 539 nm.

In some embodiments, the combination of a notch filter and a short passfilter can be used to enhance the color perception of a deuteranope.Referring to FIG. 6A, the notch filter of the first eye has a rejectionband between 470-590 nm, e.g., from 492 nm to 573 nm. The notch filtercreates L′-cone with responsivity curve 610 by cutting off shorterwavelengths of the L-cone while retaining responsivity of the S-cone.

Referring to FIG. 6B, the short-pass filter can have a cutoff wavelengthof around 550-600 nm, e.g., 564 nm. The short-pass filter leaves S-coneresponsivity intact and creates an M′-cone with responsivity curve 620by cutting off the longer wavelengths of L-cone.

A tritanope has difficulty perceiving the difference between blue andyellow caused by lack of S-cone functionality, which is responsible forperception of blue and violet in a trichromat. Similar to a protanope ora deuteranope, an appropriate set of filters can be applied totritanope's eyes to create a difference in effective spectralresponsivity of the L-cone between the left and the right eye. In thiscase, the strategy is to effectively make the L-cone in one eyesensitive only to the shorter wavelengths of the L-cone, and L-cone inthe other eye sensitive only to the longer wavelengths of the L-conewhile minimizing the change in responsivity of the M-cone.

An example of filter transmission characteristics desirable for atritanope can be achieved by the following. Referring to FIGS. 7A and7B, plot 700 shows portions of normalized responsivity 220 and 230 of M-and L-cone from FIG. 2, but omits normalized responsivity of S-cone 210,as a tritanope does not have functioning S-cones. The objective is againto create a third responsivity curve from that of the two cones, whereinthe resulting peaks of the three curves are separated from each other.Such filtering can be achieved by using short-pass filter 730 with itstransmission window marked by the labeled dotted box, which passeswavelength shorter than a cutoff wavelength, and long-pass filter 740with its transmission window marked by the labeled dotted box, whichpasses wavelength longer than a cutoff wavelength. By selecting ashort-pass filter with a cutoff wavelength around 611 nm and placing itin front of the first eye, the filter modifies the effective spectralresponsivity of the L-cone, turning it into a M′-cone with modifiedresponsivity curve 710. By selecting a long-pass filter with a cutoffwavelength slightly longer than that of the short-pass filter 730 (e.g.,622 nm) and placing it in front of the second eye, the filter 730modifies the effective spectral responsivity of its L-cone, turning itinto an L′-cone with modified responsivity curve 720. In this example,the M-cone effectively functions as an S′-cone, as its peak wavelengthis shorter than the M′- and the L′- cones. Therefore, we haveeffectively created S′-, M′- and L′-cones in the respective eyes byperforming a differential spectral filtering between the two eyes.

While the foregoing discussion refers primarily to restoring a thirdcone-like perception to a dichromat, the techniques can be applied to atrichromat to further divide up the response of the S-cone into twodifferent spectra, or alternatively the M or L cone. This can enabletetrachromacy, where two different spectral colors that appear the same(i.e., metamers) are distinguished by a human observer wearingappropriate color perception-enhancing glasses. In general, one or moreof the user's three cones can be divided into two or more separatespectra over each eye so that a person could potentially perceive 6 ormore different spectral bands instead of the normal 3.

An example of filter transmission characteristics that can enabletetrachromacy can be achieved by the following. Referring to FIG. 8A,plot 800 shows portions of normalized responsivity 210, 220, and 230 ofS-, M-, and L-cone from FIG. 2. Referring to FIG. 8A, the notch filter830 of the first eye has a rejection band from around 439 nm to 490 nm.The notch filter creates a fourth-cone with responsivity curve 810 bycutting off longer wavelengths of the S-cone while retainingresponsivity of the M- and the L-cone.

Referring to FIG. 8B, the long-pass filter 840 can have a cutoffwavelength near the lower cutoff of the notch filter 830, e.g., 448 nm.The long-pass leaves M- and L-cone responsivities intact and creates anS′-cone with responsivity curve 820 by cutting off the shorterwavelengths of the S-cone. Therefore, we have effectively created afourth-cone and an S′-cone in addition to the original M- and L-cone inthe respective eyes by performing a differential spectral filteringbetween the two eyes, potentially enabling tetrachromacy.

Various pairs of spectral filters for the first and second eyes of auser of the eyeglasses 100 have been discussed. A person typically has avisually dominant eye and a non-dominant eye. As such, various filterssuch as short-pass filters, long-pass filters, or notch filters may beassigned to a specific eye based on various considerations to improvevisual perception of the user. For example, it may be advantageous toallow more light to enter the dominant eye relative to the non-dominanteye. As such, filters can be assigned such that light to thedominant-eye is attenuated to a lesser degree than the light to thenon-dominant eye. Amount of attenuation may be compared, for example,based on the fraction of the visual spectrum being blocked by a filter.As another example, a notch filter may be assigned to the dominant eye,as notch filters typically filters out a smaller portions of the visiblespectrum, resulting in more light reaching the dominant eye.

In general, a variety of different types of spectral filters can beused. In some embodiments, the spectral filters included with lenses 110and 120 are dichroic filters. Generally, such filters can be formed frommultilayer coatings deposited on a substrate (e.g., a glass or plasticsubstrate), such as a lens blank.

Other types of spectral filters can also be used. For example, in someembodiments, lenses 110 and 120 can include absorptive filters. Examplesof absorptive filters are plastic or glass substrates impregnated withdyes, organic compounds, or inorganic compounds responsible forspectrum-sensitive absorption of light.

In certain embodiments, the spectral filtering is performed by adhesivelaminate films including organic or inorganic films. Such films mayprovide spectral filtering through dichroic filtering (e.g., using amultilayer structure) or spectrum-sensitive absorption.

In some implementations, color perception enhancing eyeglasses caninclude additional features to control unwanted reflection associatedwith the spectral filters. Dichroic filters, for example, block certainwavelengths by reflecting light at those wavelengths. Typically, lightat the blocked wavelengths incident on either side of the lens isreflected. Accordingly, one problem with dichroic filters is anundesired reflection of light incident from behind the wearer enteringthe wearer's eyes. Accordingly, eyeglasses can include additionalfeatures to reduce this effect. For example, in some embodiments,physical light stops can be used to physically block stray lightoriginating from behind the wearer from reaching the back surface of thelens. Referring to FIG. 9, this can be done by shielding the sides ofeyeglasses 900 using side shield 910 similar to that of glacier glassesor safety goggles, for example.

Referring to FIG. 10, another solution is to integrate an absorptivecircular polarizer 1030, e.g., on the eye-facing surface of lens 1000 incombination with reflective color filter 1010 (e.g. dichroic filters) onthe opposite surface. Absorptive circular polarizer 1030 includes anabsorptive linear polarizer 1031 followed by quarter-wave plate 1032with its fast or slow axis oriented at 45 degrees with respect to thetransmission axis of the absorptive linear polarizer. The incident lightentering from the front of the wearer passes first through thereflective color filter 1010, through the substrate 1020, then throughthe circular polarizer, first through the quarter-wave plate 1032, thenthrough the linear polarizer 1031. Such configuration absorbs,nominally, 50% of the unpolarized incident light from the front of thelens. On the other hand, light entering from the backside of the lensfirst enters the circular polarizer through absorptive linear polarizer1031 followed by quarter-wave plate 1032. The incident light at thispoint has lost nominally 50% of intensity, and has become circularlypolarized. The circularly polarized light travels through the substrate1020, and a certain spectral portion (corresponding to the blockwavelengths of the filter) of this light is then reflected by thereflective filter on the front surface. This reflection changes thehandedness of the circularly polarized light. The reflected light passesagain through the substrate 1020, then enters the circular polarizer inreverse. During this propagation in the reverse direction, thequarter-wave plate converts the circularly polarized light back intolinearly polarized light, but the resulting linear polarization is now90 degrees rotated with respect to the linear polarizer's transmissionaxis due to the light's double-pass through the quarter-wave plate andthe reversal of the handedness upon reflection. Therefore, the backwardincident light is completely absorbed, eliminating the glare coming frombehind the wearer.

While color-perception enhancing eyeglasses has been described,color-perception enhancing filter set can be implemented in other formsof eyewear, including contact lenses, intraocular lenses, and goggles.

In certain implementations, use of color-perception enhancing eyewearcan include training the wearer by providing objects having colorsselected to specifically correspond to the different spectraltransmission characteristics of the filter set. For example, for thefilter set shown in FIG. 3 above, the wearer can be trained using afirst object that stimulates M′ but not L′, and a second object thatstimulates L′ but not M′. By viewing the two objects sequentially and/orsimultaneously, and with knowledge of which is which, the wearer cantrain themselves to distinguish between the two different colors.

Spectral filters can also be formed using polarizers in conjunction witha dispersive birefringent material. For example, in some embodiments, aspectral filter can be formed by a pair of absorptive linear polarizers(e.g., iodine stained PVA based polarizers) separated by a layer of adispersive birefringent material (e.g., a liquid crystal or birefringentpolymer). In such structures, when illuminated with broadband,unpolarized light, the transmission spectrum depends on the amount ofretardation experienced by each wavelength as it traverses thebirefringent material and the relative orientation of the transmissionaxes of the two linear polarizers. The transmission spectrum canselected based on judicious selection of these parameters.

Spectral filters can also be formed using a wavelength-sensitivepolarizer. For example, in some embodiments, a pair of crossed polarizercan be implemented using a wavelength-selective (e.g., dispersive)linear polarizer followed by a broadband linear polarizer. Thewavelength-selective polarizer may have a polarization efficiency thatvaries over the wavelengths. Wavelengths that are efficiently polarizedby the wavelength-selective polarizer are more effectively blockedrelative to the wavelengths that are not polarized or less-efficientlypolarized. For example, a first band of wavelengths that are efficientlypolarized by the wavelength-selective polarizer may be efficientlyfiltered out by the crossed broadband linear polarizer, resulting in lowtransmission of the first band of wavelengths. As such, the transmissionspectrum can selected based on judicious selection of the spectralresponse of the wavelength-selective linear polarizer.

In general, the spectral filters described above can be formed in avariety of different ways, depending on their composition. For example,in some embodiments, thin film deposition techniques can be used to formfilters composed of dielectric multilayers on the surface of each lens.Various physical and/or chemical deposition processes can be used suchas, for example, sputtering deposition methods, evaporation depositionmethods (e.g., thermal, laser assisted, or electron beam evaporation),physical vapor deposition, chemical vapor deposition (e.g.,plasma-enhanced CVD, atomic layer deposition). Commonly-used materialsused for optical thin films include titanium oxide, silicon nitride, orsilicon oxide, for example.

In some embodiments, filters can be formed separately and laminated ontoa lens surface. For example, a laminate composed of a thin film stackcan be formed separately and laminated to the lens surface using anadhesive. As another example, an absorptive color filter can be cast asa film and laminated onto the lens surface. For instance, filmscontaining light absorbing dyes (e.g., commercially-available dyes, suchas those sold by Epolin, Newark, N.J.) can be formed using conventionalfilm forming techniques (e.g., coating, casting, extruding) and thenlaminated onto a lens. Polarizing filters, such as those describedabove, can also be applied as laminate structures.

In some embodiments, films containing light absorbing dyes can be formeddirectly on a lens surface, e.g., by casting.

In certain embodiments, the lenses themselves can include materials thatserve to spectrally filter light. For example, light absorbing dyes canbe incorporated into the lens material.

In the foregoing embodiments, each of the user's eyes view theirenvironment through a different spectral filter that covers their entirefield of view of each lens. However, other implementations are alsopossible. For example, in some embodiments, more than one spectralfilter can be used for each eye. Referring to FIG. 11, for instance, apair of eyeglasses 1100, which includes frames 101, features lenses 1110that each have a spectral filter array. Here, each array is composed oftwo different spectral filters, identified as filters a and filters b inthe inset. Filters a, for example, can each be a long pass filterdescribed above, while filters b can each be the corresponding shortpass filter (see, e.g., FIGS. 3, 4, and 7A-B). Alternatively, filters acan each be a notch filter (see, e.g., FIG. 5A and FIG. 6A) whilefilters b are each a short-pass filter (see, e.g., FIG. 5B and FIG. 6B).In some embodiments, filters a are notch filters (see, e.g., FIG. 8A),while filters b are long pass filters (see, e.g., FIG. 8B).

Generally, the filter elements are sized so that discrete areas of thewearer's retina samples light from one of the filters, but collectively,the retina samples light from both types of filter. In some embodiments,the filters have an area in a range from about 1 mm² to about 50 mm²(e.g., about 2 mm² or more, about 5 mm² or more, about 10 mm² or more,such as about 40 mm² or less, about 25 mm² or less).

While filters a and b are shown as square filters in FIG. 11, moregenerally, other shapes are possible, e.g., rectangles, hexagons, etc.Furthermore, the size and shape of the filters in a filter array canvary. For example, smaller filter array elements can be used closer tothe lens axis, while larger elements can be used closer to the lensperiphery.

Spectral filter arrays can be formed using a variety of techniques. Forexample, masked deposition techniques can be used in order to depositlayers of differing thickness and/or composition on different areas of alens surface. Other patterning techniques, such as printing techniques(e.g., ink jet printing) are also contemplated.

The above embodiments all feature passive spectral filters. In certainembodiments, however, dynamic spectral filters can be used. Generally,dynamic spectral filters are filters with an optical response thatvaries depending on some external stimulus. Electrically-switchablespectral filters, for instance, have optical properties that vary inresponse to an applied electric field. An electrically-switchablespectral filter may be implemented, for example, using liquid crystals.Photochromic spectral filters are also possible. Such filters haveoptical properties that vary depending on environmental light intensity(e.g., their properties may vary depending on whether it's daytime ornighttime). Mechanically-adjusted spectral filters are also possible, inwhich relative locations or orientations of one or more optical elementscan be adjusted to control the optical response. For example, therelative orientation of two optical elements can be adjusted (e.g.,polarization axes of a pair polarizers) to control the optical response.As another example, relative locations of two optical elements may bevaried, or relative location or orientation (e.g., incidence angle) ofthe optical element with respect to the eye of the user may be varied tocontrol the optical response.

Generally, the switchable optical property of a dynamic spectral filterscan vary depending on the type of filter used. In some embodiments, thespectral band edges of the filter can vary in response to the stimulus.Alternatively, or additionally, dynamic spectral filters can switchbetween a first state in which they provide spectral filtering, and asecond stage in which they exhibit the same transmission propertiesacross the entire visible spectrum, i.e., they appear colorless.

Referring to FIG. 12, a pair of eyeglasses 1200 includes a dynamicspectral filter (1210 and 1220) with each lens. Eyeglasses 1200 includeframes 1201 that feature a filter controller 1230 attached to one of theframes' arms. Controller 1230 includes a power supply and controlelectronics in communication with dynamic filters 1210 and 1220, e.g.,via an electrical connection, such as wire leads. During operation,controller 1230 directs electrical signals to each of the dynamicfilters to control (e.g., vary) the spectral properties of each filter.

Generally, the spectral properties of dynamic filters 1210 and 1220 canbe varied depending on one or more different external inputs, such asdirect control from the user (e.g., using a control switch or other userinterface), or in response to input from a sensor (e.g., a lightintensity sensor, a spectral sensor, a proximity sensor, a GPS sensor,etc.). The sensor can be mounted on frames 1201 (e.g., incorporated incontroller 1230) or can be separate. In some cases, separate sensors canbe part of another device, such as a smartphone.

In some embodiments, a first optical sensor may be placed before thedynamic filters 1210 and 1220 (e.g., on the outer surface of theeyeglasses 1200 facing away from the user) and a second optical sensormay be placed after the dynamic filters 1210 and 1220 (e.g., on theinner surface of the eyeglasses 1200 facing the eye of the user). Thefirst and second optical sensors can be used to measure the intensityand/or spectrum of the light before and after the dynamic filters 1210and 1220. The pre-filter and post-filter spectra may be analyzed by thecontroller 1230 to dynamically control the spectral properties of thedynamic filters 1210 and 1220. For example, specific color recognitioncapabilities of the user of the eyeglasses 1200 may be taken intoaccount by the controller 1230 in controlling the dynamic filters 1210and 1220 to optimize the color perception of the user. As anotherexample, illumination intensity or color temperature of a visual scenemay be determined and dynamically compensated by the controller 1230. Asyet another example, the controller 1230 may determine various scenessuch as a monochromatic scene (e.g., a green field of grass) or acolorful scene, and adjust the dynamic filters 1210 and 1220 to optimizethe color perception of the user.

In some embodiments, the spectral properties of the dynamic filters 1210and 1220 can be varied in a set sequence to enhance color perception ofthe wearer. For example, the spectral characteristics of the filters1210 and 1220 may be toggled between a first state and a second state ata set frequency. The frequency may be, for example, a frequency at whichvisual changes can be sufficiently perceived by the human vision (e.g.,less than 24 Hz, less than 30 Hz). Such toggling may, under certainvisual conditions, help the wearer differentiate colors as a perceivedchange in contrast, hue, saturation or color. In general, the togglingmay be generalized to cycling through three or more states.

A variety of different technologies can be used for dynamic spectralfiltering. For example, electrochromic or liquid crystal based spectralfilters can be used. Electrically-switchable Bragg gratings, such asthose formed used polymer-liquid crystal composites, can be used. Insome embodiments, the dynamic spectral filters 1210 and 1220 may beimplemented using mechanical actuation. For example, micro-motormechanisms (e.g., micro voice coil) or piezoelectric actuators may beused to mechanically actuate the spectral filters 1210 and 1220 todynamically vary the spectral properties of the filters.

In some embodiments, a manual mechanical adjustment mechanism may beimplemented to provide various static adjustments. For example, thefocus of the eyeglasses 1200 may be varied based on a mechanicaladjustment mechanism by adjusting the relative location of opticalelements of compound lenses of the eyeglasses 1200. As another example,overall transmissivity of the eyeglasses 1200 may be varied based on amechanical adjustment of the alignment of the crossed polarizers.

EXAMPLE

Dichroic coated glass filters were obtained from Rosco (Stamford,Conn.). Specifically, the filters were filter #1065, 5401, and 5600. Thefilter specifications are included as Appendices I-III. Rosco #1065 is ashort-pass filter with a cutoff around 550 nm, while #5401 and #5600 arelong-pass filters with cutoffs around 550 nm and 580 nm, respectively.

The glass filters were cut into shape of a lens and fitted onto a pairof eyeglasses frames. The first filter set was Rosco #1065 and #5600,and the resulting modified M-cone responsivity curves 1310 and 1320(corresponding to M′- and L′-cones, respectively) are shown in FIG. 13A.

The second filter set was Rosco #1065 and #5641, and the resultingmodified M-cone responsivity curves 1330 and 1340 (corresponding to M′-and L′-cones, respectively) are shown in FIG. 13B. Filter set 1 providedfurther separation of the peaks of M′ and L′ cones but larger differencein the relative peak responsivity, while filter set 2 provided lessseparation of the peaks but more balanced peak responsivity.

The subject (and inventor), a confirmed protanope, tested the glasses byobserving different colored objects with and without the eyeglasses. Thesubject reported an enhanced perception of color that is described as‘shimmering’ of color, color ‘popping out’, and color ‘jumping out’. Thesubject also reported that filter set 2 provided better enhancedcolor-perception over filter set 1.

The subject was further tested using multiple widely-acceptedpseudoisochromatic color vision tests, including the Cambridge ColorTest, the Farnsworth D-15 test, and the Hardy Rand and Rittler (HRR)test. While the subject did not gain any apparent improvement in theCambridge Color Test, substantial improvements in the result of theFarnsworth D-15 and the HRR color tests were observed.

Farnsworth D-15 test is one of the standard suite of tests used inevaluating color blindness. It involves having a subject order 15 blockof different shades of color by picking the most similar color startingfrom a shade of blue. A metric named the color confusion index (CCI) isused to assess the severity of a color blindness condition. CCI isdefined as the ratio of the measured Bowman's total color differencescore (TCDS) of the test subject over the TCDS of a normal trichromat.See, e.g., Bowman K J: A method for quantitative scoring of theFarnsworth panel D-15. Acta Ophthalmol 60:907, 1982. Therefore, aperfect normal trichromat would score 1.0, and a nominal dividing linebetween a normal and defective color vision is accepted to be 1.60. See,e.g., A. J. Vingrys, P. E. King-Smith; A quantitative scoring techniquefor panel tests of color vision. Invest. Ophthalmol. Vis. Sci.1988;29(1):50-63.

The subject was tested by performing the test twice without thecolor-perception enhancing eyeglasses and scored a color confusion indexof 2.51 on the first trial and 2.99 on the second trial. The subject wasthen tested with the eyeglasses, performing 5. On these tests, thesubject scored 1.79, 1.82, 1.05, 1.19, and 1.38, in that order. The datadisplayed a clear improvement of the CCI, scoring below 1.60 of a normalcolor vision in three out the five trials. Upon further inspection ofthe data, a significant drop in CCI after the first two trials becomeapparent. The drop was attributed to the learning and adjustment by theinventor to the new perception enabled by the glasses. The subjectlearned the correct perception of color by learning the correct answersto his mistakes, and conditioning on that knowledge to improve hisperformance. Such conditioning and learning enabled the subject to scorewithin the normal color vision threshold.

Similarly, the subject was able to significantly improve his performancein the HRR test from getting around 2-3 correct out of 14 to getting 8-9out of 14 with practice using the eyeglasses.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. An article, comprising: a first ophthalmic lenscomprising a first spectral filter; and a second ophthalmic lenscomprising a second spectral filter, wherein the first spectral filtersubstantially blocks visible light having wavelengths corresponding to afirst portion of a spectral sensitivity range of a first type of coneand substantially passes visible light having wavelengths in a second,non-overlapping portion of the spectral sensitivity range, and thesecond spectral filter substantially blocks visible light havingwavelengths in the second portion of the spectral sensitivity range andsubstantially passes visible light having wavelengths in the firstspectral sensitivity range.
 2. The article of claim 1, wherein thearticle is eyeglasses, a pair of contact lenses, goggles, or a pair ofintraocular lenses.
 3. The article of claim 1, wherein the first andsecond spectral filters are a low-pass filter and a high-pass filter,respectively.
 4. The article of claim 1, wherein at least one of thefirst and second spectral filters is a notch filter.
 5. The article ofclaim 1, wherein at least one of the first and second spectral filterssubstantially transmits visible light having wavelengths below 520 nm.6. The article of claim 5, wherein both of the first and second spectralfilters substantially transmits visible light having wavelengths below520 nm.
 7. The article of claim 1, wherein the first and second spectralfilters are reflective spectral filters.
 8. The article of claim 1,wherein the first and second spectral filters are absorptive spectralfilters.
 9. The article of claim 1, wherein the first and secondspectral filters are passive spectral filters.
 10. The article of claim1, wherein the first and second spectral filters are dynamic spectralfilters.
 11. The article of claim 10, wherein the dynamic spectralfilters each comprise an electro-optic element.
 12. The article of claim1, wherein at least the first ophthalmic lens further comprises a filterarray comprising the first spectral filter.
 13. The article of claim 12,wherein the second ophthalmic lens further comprises a filter arraycomprises the second spectral filter.
 14. The article of claim 1,wherein a first transmission spectrum of the first spectral filter and asecond transmission spectrum of the second spectral filter areconfigured to enhance the color perception of a dichromat.
 15. A methodof enhancing the color perception of a dichromat, comprising: providingthe dichromat with the article of claim
 1. 16. The method of claim 15,wherein the dichromat is a protanope and the first type of conecorresponds to an M-cone.
 17. The method of claim 15, wherein thedichromat is a deuteranope and the first type of cone is an L-cone. 18.The method of claim 15, wherein the dichromat is a tritanope and thefirst type of cone is a S-cone.